A character invented by Plato, used in a few of his less successful dialogs (for example, Laws). Maybe he did it because he was tired of making Socrates talk all the time, you know, like a ventriloquist trying out a new dummy. In the end, most commentators agree that it was a very lame strategy. One thing that makes it weird is that everybody has a name except this one guy, who they call "Athenian Stranger" for short.